#include<iostream>
#include<string>
#include<map>
using namespace std;
typedef long long LL;
int n;
string s1, s2, s3;
int main()
{
	cin >> n;
	cin >> s1 >> s2 >> s3;
	string ans;
	for (int i = 0; i < n; i++) {
		char a = s1[i];
		char b = s2[i];
		char c = s3[i];
		if (a != b && b != c) ans += a;
		else if (a == b && b == c)ans += a;
		else if (a == b && b != c)ans += a;
		else if (a == c && b != c)ans += a;
		else if (b == c && a != b)ans += b;
	}
	LL res = 0;
	for (int i = 0; i < n; i++) {
		char a = s1[i];
		char b = s2[i];
		char c = s3[i];
		if (a != ans[i])res++;
		if (b != ans[i])res++;
		if (c != ans[i])res++;
	}
	cout << res << endl;
	return 0;
}